on hardmode there's actually an arrow that tells you where the spray starts. Helps you orient yourself to the patterns above. The arrow isn't there on normal so I imagine that's just blizzard saying the spray doesn't matter. In normal as long as you don't move around a lot you shouldn't get shot more than once or twice per dreadspray. Easily healable.

better tactic is to ignore them for the whole time. It will make this fight much shorter (~8min)

Wouldn't agree with that for a guild pushing for their first normal mode kill. Via the platform orbs mana is infinite and there's no ramp up on add spawns. As a progressing guild what is gained by burning the boss and risking plateauing the dps at a certain point where the players are unable to optimise dps?

Seen the strat work on beta LFR. It's necessary for heroic mode. But I'd never consider it as a viable option for a first time guild.